Alkylation of N,N-Dibenzylaminoacetonitrile: From Five- to Seven-Membered Nitrogen-Containing Heterocyclic Systems.

The syntheses of several alkaloids and nitrogen-containing compounds including N-Boc-coniine (14b), pyrrolizidine (1), δ-coniceine (2), and pyrrolo[1,2a]azepine (3) are described. New C-C bonds in the α position relative to the nitrogen atom were formed by the alkylation of metalated α-aminonitriles 4 and 6a-c with alkyl iodides possessing the requisite size and functionality. In all of the reported cases, the pyrrolidine ring was formed in the aqueous medium through a favorable 5-exo-tet process involving a primary or a secondary amino group and a terminal δ-leaving group. Conversely, the azepane ring was efficiently formed in N,N-dimethylformamide (DMF), as the preferred aprotic solvent, through an unreported 7-exo-tet cyclization process involving a more nucleophilic sodium amide and a terminal mesylate borne by a saturated six carbon chain unit. In this way, we successfully synthesized pyrrolo[1,2a]azepane 3 and 2-propyl-azepane 14c in good yields from inexpensive and readily available materials without tedious separation methods.

Prodrugs as new therapies against Chagas disease: in vivo synergy between Trypanosoma cruzi proline racemase inhibitors and benznidazole.

OBJECTIVES: Chagas disease, caused by the parasitic protozoan Trypanosoma cruzi, affects approximately 6-7 million people worldwide. There are limited available therapies and they exhibit low efficacy, often high toxicity in chronic cases and some drug resistance. In this study, our objective was to develop ester prodrugs that inhibit proline racemase (TcPRAC), a parasitic enzyme previously identified and characterised as a promising target because of its essential role in the parasite's life cycle and virulence, and to test their activity against T. cruzi. METHODS: Using structural bioinformatics, we modelled several functional intermediates of the catalytic site between the opened and closed conformations of TcPRAC based on its crystal structures in complex with its competitive inhibitor, pyrrole-2-carboxylic acid. Guided by these intermediates, which were later validated in cocrystals, we designed and evaluated numerous compounds and tested them enzymatically on live parasites and in mice with our quick and straightforward drug screening method, which is based on state-of-the-art bioluminescent T. cruzi parasites injected subcutaneously. RESULTS: Some of our novel compounds specifically inhibited racemase activity, as determined through biochemical assays, and covalently bound to TcPRAC. Furthermore, the corresponding ester prodrugs were effective in killing parasites in vitro. Bioluminescent T. cruzi assays in mice showed that JR1531, a TcPRAC inhibitor prodrug, can kill parasites in living animals, with boosted action when combined with low doses of benznidazole. CONCLUSION: This approach, based on TcPRAC inhibitor prodrugs in association with low doses of benznidazole, may lead to more effective, specific and non-toxic therapies against Chagas disease.

Designed mono- and di-covalent inhibitors trap modeled functional motions for Trypanosoma cruzi proline racemase in crystallography.

Chagas disease, caused by Trypanosoma cruzi, affects millions of people in South America and no satisfactory therapy exists, especially for its life threatening chronic phase. We targeted the Proline Racemase of T. cruzi, which is present in all stages of the parasite life cycle, to discover new inhibitors against this disease. The first published crystal structures of the enzyme revealed that the catalytic site is too small to allow any relevant drug design. In previous work, to break through the chemical space afforded to virtual screening and drug design, we generated intermediate models between the open (ligand free) and closed (ligand bound) forms of the enzyme. In the present work, we co-crystallized the enzyme with the selected inhibitors and found that they were covalently bound to the catalytic cysteine residues in the active site, thus explaining why these compounds act as irreversible inhibitors. These results led us to the design of a novel, more potent specific inhibitor, NG-P27. Co-crystallization of this new inhibitor with the enzyme allowed us to confirm the predicted protein functional motions and further characterize the chemical mechanism. Hence, the catalytic Cys300 sulfur atom of the enzyme attacks the C2 carbon of the inhibitor in a coupled, regiospecific-stereospecific Michael reaction with trans-addition of a proton on the C3 carbon. Strikingly, the six different conformations of the catalytic site in the crystal structures reported in this work had key similarities to our intermediate models previously generated by inference of the protein functional motions. These crystal structures span a conformational interval covering roughly the first quarter of the opening mechanism, demonstrating the relevance of modeling approaches to break through chemical space in drug design.

Solid-phase synthesis and evaluation of libraries of substituted 4,5-dihydropyridazinones as vasodilator agents.

The solid-phase parallel preparation of a library of 4,5-dihydropyridazin-3(2H)-one derivatives substituted at position 6 with piperazinylmethyl or tetrahydroquinolinylmethyl groups and analogues (3) is reported. Polymer-supported gamma-keto-delta-aminoesters prepared from Wang resin reacted with hydrazine or methylhydrazine to afford pyridazinones in good yields after a cyclization cleavage approach. We have evaluated these novel analogues and several compounds of other series (1, 2) for their vasorelaxant effect. Among the products tested, 3l and 3d proved to be efficacious and potent relaxant agents of the isolated rat aorta. Inhibitors of phosphodiesterase (PDE3), responsible for the breakdown of cyclic AMP in the vascular smooth muscle, are currently developed for cardiac heart failure because of their inotropic effect and coronary vasodilatation. We had expected that the vasodilatation induced by 3l, as efficient as reference PDE3 inhibitors, milrinone or CI-930, to be due to PDE3 inhibition. However 3l and 3d exhibited a low inhibitory effect against PDE3 isoenzyme activity. These compounds induced a significant vasorelaxation, which could be of therapeutic interest even if their mechanism of action remains to be determined.

Synthesis and potential anti-inflammatory activity of some tetrahydrophthalazinones.

A solid-phase route for the preparation of 4a,5,8,8a-tetrahydrophthalazinon-1-ones employing the Diels-Alder reaction has been developed. Some of the new compounds have been tested for inhibition of LPS-stimulated TNF-alpha production in human whole blood from patients with chronic obstructive pulmonary disease (COPD). This evaluation revealed two compounds 17 and 18 of interest, incorporating an arylpiperazine moiety, which were found to inhibit LPS-induced TNF-alpha release like the well known anti-inflammatory PDE4 inhibitors, rolipram and roflumilast.